Abstract: Soil organic carbon (SOC) in alpine grasslands are largely affected by topography-induced variability,which may exert large uncertainties to the regional estimation of SOC stock. In this study,we totally investigated 9 transects within 3 elevation zones in grasslands of the middle Qilian Mountains. The variation of SOC by elevation,slope aspect,and slope position were studied to further explore the relationships between SOC density and environmental factors. Results showed that the SOC at 0~60 cm in grasslands of the middle Qilian Mountains varied from 9.98 to 38.96 kg·m^-2,with an average density of 22.31 kg·m^-2. Among different elevation zones,the highest SOC density occurred at an elevation zone of 3 350 m (37.70 kg·m^-2),which was 2.07 and 3.41 times larger than that at the 2 900 m and 2 450 m,respectively. In sloping areas,SOC density on the west-facing slopes was higher than that on the south- and southwest-facing slopes. SOC density at gully was significantly higher than that at summit and the upper,middle,and lower positions of sloping areas. The regression analysis suggested that SOC density showed the closest relationship with soil water content with the coefficient of determination (R²) close to 0.85. The general linear model suggested that the proportion of the total variation of SOC density explained by topography reached 90.68%,of which 71.82% and 15.78% were attributed to elevation and slope position,respectively. Our results highlighted the importance of topographic factors in shaping the spatial patterns of SOC in grasslands of the middle Qilian Mountains,and suggested that the topographic factors,especially the elevation and slope position,should be given priority in the construction of SOC storage estimation model in grasslands of this region.

Key words: Soil organic carbon, Grasslands, Topography, The Qilian Mountains

摘要： 本文通过调查祁连山中段草地3个海拔段共9条样带，研究了土壤有机碳随海拔、坡向、坡位的分布特征及环境影响因素。结果表明，祁连山中段草地0~60 cm土壤有机碳密度变化范围为9.98~38.96 kg·m^-2，均值为22.31 kg·m^-2。不同海拔间，3 350 m土壤有机碳密度最大，分别是2 900 m和2 450 m处的2.07和3.41倍；在山坡区域，西坡土壤有机碳密度高于南坡和西南坡；沟谷显著高于坡顶和山坡的上、中、下坡位。回归分析表明，土壤有机碳密度与土壤含水量的关系最密切，回归方程的复相关系数（R²）达0.85。一般线性模型表明，地形对0~60 cm土壤有机碳密度空间变异的解释率高达90.68%，其中海拔和坡位分别贡献了71.82%和15.78%。因此，在构建该区草地土壤有机碳储量估算模型时，应重点考虑海拔和坡位因子的指示性。

关键词: 土壤有机碳, 草地, 地形, 祁连山